Although the Prophet (s) was born in the polytheistic society of Arabia, he never worshiped any idols, and avoided the inappropriate manners that were rampant in pre-Islamic Arabia. He (s) was chosen by God as His messenger at the age of forty. His most important message was the invitation to monotheism and the goal of his mission was the perfection of humanity's moral virtues. Although the polytheists of Mecca persecuted him and his followers for many years, neither he, nor his followers gave up following Islam. After thirteen years of preaching in Mecca, he immigrated to Medina. This immigration (Hijra) marked what became the beginning of the Islamic calendar. In Medina, he dealt with many wars imposed by the polytheists, however, in all of them, the eventual victory belonged to Muslims.

Because of the efforts of the Prophet (s), the pre-Islamic age of ignorance in Arabia transformed into a monotheistic society in a short time. Towards the end of the Prophet's (s) life, almost everyone in the Arabian Peninsula had become Muslim. The number of Muslims continued to grow throughout the centuries, and Islam is now the fastest growing religion in the world. The Prophet (s) advised Muslims to adhere to the teachings of the Qur'an and the Ahl al-Bayt (s) and not to abandon them. He made note of Imam 'Ali (a) as his successor in various events throughout his life, including the event of Ghadir.